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Milk comparisons not so straightforward

Reviewing almost 200 publications, the researchers concluded that previously conducted controlled studies investigating whether differences exist between organic and conventionally produced milk have so far been largely ambiguous, due principally to the complexity of the research question and the number of factors and variables that can influence milk composition.

“This review presents one of the most detailed treatises to date of organic versus conventional milk composition,” said Dr Matt Lucy, a professor of animal science at the University of Missouri and editor-in-chief of the Journal of Dairy Science.

“When comparing organic and conventional milk composition (especially milk fatty acids), previous studies have generally compared organic dairying with milk produced from grass-fed cows to conventional dairying with milk produced from concentrate-fed cows. The differences in milk composition observed are actually due to the different diets of the cows (ie, pasture versus concentrate feeding) rather than organic versus conventional farming systems,” according to lead investigator Dr Don Otter, senior scientist for Food & Bio-Based Products at the AgResearch Grasslands Research Centre in New Zealand.

Because there are many factors that affect milk composition, it is difficult to control for all of them when comparing organic to conventional milk production.

According to the investigators, “The term ‘organic,’ when applied to dairying, is not universal and, to a large extent, is defined simply by regulations that differ from one country to the next. ‘Conventional’ basically is anything that is not ‘organic.’

“However, in most parts of the world, conventional dairying is associated with high levels of grain feeding, the use of cow breeds which produce high milk volumes and the application of large amounts of fertilizer (‘high input’ farming), while organic dairying is tied to pasture and forage feeding, lower amounts of fertilizer application and the use of mixed or minority breeds (‘low input’). The vast majority of differences reported between organic and conventional milk come from what cows are fed and their breed and is not anything unique to being organic or conventional in itself.”

Therefore, the review concluded that in terms of nutrients in milk, there is nothing distinct about organic milk that makes it unique from conventionally produced milk once the different factors that influence milk production are compared or adjusted for. If animal genetics, health, breed, diet, management and/or environment differ, then so will the composition of the milk produced.

Journal reference:

B.H. Schwendel, T.J. Wester, P.C.H. Morel, M.H. Tavendale, C. Deadman, N.M. Shadbolt, D.E. Otter
Published online: December 11, 2014